It is presently known that in many mechanical applications, the machined finish of a surface is of vital importance. For example, finishes must be maintained to close tolerances in bearings, races, cylinder walls, and the like. That close tolerance finishes are an everyday requirement in industry is evidenced by the fact that the Bureau of Standards has published classifications or standards for surface finishes. These classifications are graduated from designations of zero through fifty, the lower the designation, the smoother the finish. The standards are set with various parameters considered, such as the material of the finished surface of interest, the grit or coarseness of the finishing material, the method of finish or the like. It will be understood that there are various known finish methods, such as lapped, ground, blanchard, milled, profiled, and shape-turned.
Prior art methods of determining the finish of a surface have been of two basic types. The contacting type of sensor utilizes a stylus resolver such that the deflections of the stylus riding on the surface are converted to electrical signals indicative of surface smoothness. It will be readily appreciated that this type of measurement is akin to the stylus of a phonograph riding in a record groove. In use, the stylus-type resolvers measure deflections over a fixed area or lineal distance to determine surface finish.
There have also been previously known noncontact finish sensors, principally of the capacitive type. Here, a capacitive sensor rides over a surface in much the same manner as a proximity sensor, the capacitance of the sensor being matched to the surface material.
It will be readily appreciated that the finish sensors of the prior art are painstaking in use, being highly sensitive and adapted for laboratory use rather than use "on line." The prior art apparata and technique are used on a test sample basis, with workpieces being randomly selected from an assembly line for test in a laboratory to determine whether the line is meeting surface finish requirements. At best, the prior art achieves only a spot-check in an assembly line environment.
The prior art has taught stylus-type transducer finish sensors in U.S. Pat. Nos. 4,106,333; 3,133,149; 3,372,578; 3,320,799; 3,733,598; 4,126,036; and 3,377,828. Types of noncontacting finish sensors are taught in U.S. Pat. Nos. 3,688,569; 4,148,027; 4,149,187; and 3,855,843. Each of the prior art finish sensors taught by the aforementioned patents has the inherent drawback of requiring a laboratory environment to attain the desired test.